Nitride semiconductors represented by gallium nitride (GaN) are semiconductors composed of nitrides of metal elements classified to Group 13 in the periodic table, and also called Group III nitride semiconductors, gallium nitride group semiconductors, etc. The nitride semiconductor is sometimes represented by compositional formulas such as (B,Al,Ga,In)N, (Al,Ga,In)N, BxAlyGazIn1-x-y-zN (where, 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦x+y+z≦1), AlxGayIn1-x-yN (where, 0≦x≦1, 0≦y≦1, 0≦x+y≦1).
Doped with impuritys, the nitride semiconductor can be electrically conductive. O (oxygen), Si (silicon), Ge (germanium), etc. are known as n-type impuritys. Mg (magnesium), Zn (zinc), etc. are known as p-type impuritys.
The nitride semiconductor is composed of a wurzite structure classified to the hexagonal crystal system.
GaN substrates are manufactured by slicing a bulk GaN crystal grown by HVPE (Hydride Vapor Phase Epitaxy) method (Patent Document 1) or ammonothermal method (Patent Document 2, Patent Document 3).
A non-polar or semi-polar GaN substrate can be obtained by a method in which a bulk GaN crystal grown along the c-axis on a C-plane sapphire substrate or a C-plane GaN substrate is sliced so that the non-polar plane or the semi-polar plane appears as a main surface (Non-Patent Document 1). This method is not suitable for manufacturing a large-area substrate although it is advantageous in that a non-polar or semi-polar GaN substrate with low stacking fault density can be obtained. Therefore, it has been recently studied to manufacture a bulk GaN crystal by a homo-epitaxial growth that uses a non-polar or semi-polar GaN substrate as a seed (Patent Document 4).
The Patent Document 4 says that the difference of impurity concentration between the GaN crystal to be grown and the seed must be 3×1018 cm−3 or less in order to homo-epitaxially grow the GaN crystal with a stacking fault density of 100 cm−1 or less by using a non-polar or semi-polar GaN substrate as a seed. This document does not describe an example for which a GaN crystal with a impurity concentration of 4×1018 cm−3 or more and a stacking fault density of 100 cm−1 or less was homo-epitaxially grown on the non-polar GaN substrate.